Methods for Adjusting the Power of an External Reader

ABSTRACT

Disclosed herein are methods and systems for adjusting the power level of an external reader of an electronic device. The external reader transmits power to the electronic device with a radio frequency electromagnetic signal. The electronic device may rectify the radio frequency electromagnetic signal and create a rectified voltage. The rectified voltage may be positively correlated to the power level transmitted by the external device. The rectified power can be used to power a component of the electronic device, such as a component configured to measure either a voltage or power associated with the rectified voltage. The electronic device may communicate the measured voltage or power back to the external reader. Based on the communicated voltage or power, the external reader may adjust its power level of the transmitted power.

BACKGROUND

Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.

Some electronic devices are of sufficiently small size that a power supply cannot reasonably accompany the device. In these instances, the electronic device may receive power from an external power source. The external power source may be configured to supply power to the electronic device wirelessly.

SUMMARY

One aspect of the present disclosure provides an apparatus. The apparatus includes an antenna configured to receive electromagnetic radiation to form a supply signal. The antenna is also configured to output a backscatter signal based on the received electromagnetic radiation. The antenna also can adjust an antenna impedance to cause a backscatter of the received electromagnetic radiation. The apparatus also includes a rectifier configured to rectify the supply signal into a supply voltage. Further, the apparatus includes a power unit configured to measure the supply voltage. Additionally, the apparatus may include a measurement unit configured to cause the antenna impedance to communicate the measured supply voltage via the backscatter of received electromagnetic radiation.

Another aspect of the present disclosure provides reader apparatus. The reader apparatus includes an antenna configured to transmit electromagnetic radiation with a power level. The antenna also is configured to receive backscatter electromagnetic radiation and output a voltage-indication signal based on the backscatter electromagnetic radiation. The reader apparatus also includes a control unit. The control unit may be configured to analyze the voltage-indication signal to determine a voltage of a device that caused the backscatter electromagnetic radiation. The control unit may also be configured to determine a voltage requirement for the device. Further, the control unit may also be configured to responsively adjust the power level based on the voltage requirement.

In yet another aspect of the present disclosure, a method is provided. The method includes receiving electromagnetic radiation with an antenna to form a supply signal. The method also includes rectifying the supply signal into a supply voltage. Another part of the method includes measuring the supply voltage with a measurement unit. Additionally, the method includes adjusting an antenna impedance based on the measured supply voltage to cause a backscatter of the received electromagnetic radiation. The backscatter of the received electromagnetic radiation is based on both the received electromagnetic radiation and the antenna impedance.

These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example system that includes an eye-mountable device in wireless communication with a reader, in accordance with an example embodiment.

FIG. 2A is a bottom view of an example eye-mountable device, in accordance with an example embodiment.

FIG. 2B is a side view of the example eye-mountable device shown in FIG. 2A, in accordance with an example embodiment.

FIG. 2C is a side cross-section view of the example eye-mountable device shown in FIGS. 2A and 2B while mounted to a corneal surface of an eye.

FIG. 2D is a side cross-section view of the example eye-mountable device when mounted as shown in FIG. 2C, in accordance with an example embodiment.

FIG. 3 is a functional block diagram of an example system for measuring a supply voltage, in accordance with an example embodiment.

FIG. 4 is a block diagram of an electrical sensor system operated by a reader to obtain a series of supply voltage measurements over time, in accordance with an example embodiment.

FIG. 5 shows an example wearer wearing two eye-mountable devices, a band, earrings, and a necklace, in accordance with an example embodiment.

FIG. 6 shows a scenario where a reader communicates with an eye-mountable device and a display device, in accordance with an example embodiment.

FIG. 7 is a flow chart of an example method, in accordance with an example embodiment.

DETAILED DESCRIPTION

One aspect of the present disclosure provides a method for adjusting the power level of an external reader of an electronic device, such as a contact lens with integrated electronics. The external reader transmits power to the electronic device with a radio frequency electromagnetic signal. The electronic device may rectify the radio frequency electromagnetic signal and create a rectified voltage. The rectified voltage may be positively correlated to the power level transmitted by the external device. This rectified power may be used to power various components of the electronic device. The rectified power can also be used to power a sensor of the electronic device configured to measure either a voltage or power associated with the rectified voltage. The electronic device may communicate the measured voltage or power back to the external reader. Based on the communicated voltage or power, the external reader may adjust its power level of the transmitted power.

Several benefits may be achieved by adjusting the transmitted power level of the external reader. First, the battery of the external reader may be preserved. The external reader may reduce the power level transmitted, thus reducing the amount of battery power used, while still continuing to maintain functionality of the electronic device. Second, the amount of electromagnetic power that is coupled into the body of a person using the electronic device may be minimized. In some embodiments, the electronic device is part of an eye-mountable device. The power level of the external reader may be chosen to minimize the amount of energy that propagates into the eye of a wearer of the eye-mountable device. Third, the power level transmitted may be reduced in order to prevent the power from interfering (e.g., jamming) nearby electronic devices operating with the same wireless frequency and/or technology. Fourth, if the power level from the external device is too high, the external device may have trouble receiving signals from the electric device. The power may be high enough that the signals communicated from the electronic device back to the external reader may be drowned out.

An external reader device or “reader” can radiate radio frequency radiation to power the sensor. The reader may thereby control the operation of the sensing platform by controlling the supply of power to the sensing platform. In some examples, the reader can operate to intermittently interrogate the sensing platform to provide a reading by radiating sufficient radiation to power the sensing platform to obtain a measurement and communicate the result.

The external reader may also include processing logic. The external reader may receive an indication of a voltage from the electric device and compare the voltage to the voltage required for certain functionality of the electronic device. For example, some functionality of the external device may run on 3.4 Volts while other functionality may require 5 Volts for correct operation. Therefore, when the external reader receives an indication of the voltage of the electronic device, it may be able to adjust its transmitted power to increase (or decrease) the voltage of the electronic device.

The sensor of the ophthalmic sensing platform can be configured with, or be part of, a Radio-frequency Identification (RFID) tag. The RFID tag and reader can communicate using an RFID protocol; e.g., an RFID Generation 2 protocol. The RFID tag can be configured to receive radio signals from the reader. In some embodiments, the reader's signals can be used for both communicating with and powering the RFID tag; while in other embodiments, the RFID tag can be a powered device; e.g., be configured with a battery that powers the tag. In embodiments, where a battery powers the tag, the reader's signals may be used to charge the battery. Therefore, the battery may be wirelessly charged in situ.

The reader can communicate with other devices than the RFID tag. As one possible example, the reader can be equipped with a Bluetooth interface as well as with an RFID interface. The reader can communicate with other devices, e.g., a display device, via a Bluetooth or other protocol. In one example, the reader can obtain data from the RFID tag using RFID command(s); e.g., the RFID Generation 2 standard Read command. Upon obtaining the data, the reader can store, process, and/or communicate the data using the Bluetooth interface to another device, such as the display device. Other interfaces for communicating with devices using other communication protocol(s) are possible as well.

As an example, the above-mentioned contact lens can be configured with a sensor that includes an RFID tag. As mentioned above, the sensor can be configured to take measurements while being worn in an eye of a wearer. Upon taking the measurements, the sensor may store data related to the measurements, and subsequently send the data upon request from the reader. The reader, in turn, can store and/or process the received data. For example, the sensor can take current measurements of a supply voltage in the tag. The reader can process the supply voltage data to determine if the supply voltage is large enough to power various components of the tag. The determination may be based on a desired functionality of the tag.

In some embodiments, the supply voltage information can be sent from the reader to a display device. The display device could be, for example, a wearable, laptop, desktop, handheld, or tablet computer, a mobile phone, or a subsystem of such a device. The display device can include a processing system; e.g., a central processing unit (CPU), and a non-transitory computer readable medium configured to store at least program instructions. One example of a wearable computer is a head-mountable display (HMD). The HMD can be a device that is capable of being worn on the head and places a display in front of one or both eyes of the wearer. The display device can store the data received from the reader, perhaps process the data, and generate display(s) based on the received and/or processed data.

In some embodiments, the reader and the display device can be configured with configuration data to perform supply voltage processing. For example, the reader can include configuration data such as current measurement data for various levels of the supply voltage. Based on this configuration data, the reader can determine if the supply voltage is high enough to power various components of the tag. Also, the wearer may provide an input to the display device to indicate a desired functionality of the tag. Based on the desired functionality of the tag, a threshold supply voltage may be needed.

During operation of these embodiments, the RFID tag in an eye of the wearer can generate supply voltage data and send the supply voltage data to the reader. The reader can then process the supply voltage data to compare it with a threshold supply voltage based on a desired functionality of the tag. Then, the display device can be configured to adjust a power level of the signal transmitted from the reader to the tag. In particular embodiments, either the reader or the display device can take supply voltage data as inputs and adjust a power level of the signal transmitted from the reader to the tag as output; i.e., all processing can take place at either the reader or display device.

In some embodiments, the reader can be configured to be worn in proximity to one or more contact lenses configured with sensors worn by a person. For example, the reader can be configured to be part of a pair of eyeglasses, jewelry (e.g., earrings, necklace), headband, head cover such as a hat or cap, earpiece, other clothing (e.g., a scarf), and/or other devices. As such, the reader can provide power and/or receive measurements while proximate to the worn contact lens(es).

In other embodiments, both the display and the reader may be combined into a single unit. For example, a device, such as a mobile phone, may have functionality to act as both the display and the reader to interact with the tag.

Configuring the reader to be frequently worn in proximity to one or more contact lenses enables the lenses to have a reliable external power source and/or storage for sensor data collection, processing of sensor data, and transmission of unprocessed and/or processed sensor data to additional devices; e.g., the above-mentioned display device. Thus, the herein-described reader can provide valuable support functionality, including but not limited to power, communication, and processing resources, to enhance use of contact lenses with embedded sensors, while enabling consequent reduction of support functions on the contact lens. This reduction of support functions on the contact lens may free resources on the contact lens to enable addition of more and/or different sensors and to provide for other functionality on the contact lens.

FIG. 1 is a block diagram of a system 100 that includes an eye-mountable device 110 in wireless communication with a reader 180. The exposed regions of the eye-mountable device 110 are made of a polymeric material 120 formed to be contact-mounted to a corneal surface of an eye. A substrate 130 is embedded in the polymeric material 120 to provide a mounting surface for a power supply 140, a controller 150, voltage sensor 160, and a communication antenna 170. The voltage sensor 160 may be operated by the controller 150 or it may operate based on receiving the DC Power 141. The power supply 140 supplies operating voltages to the controller 150 and/or the voltage sensor 160. The antenna 170 is operated by the controller 150 to communicate information to and/or from the eye-mountable device 110. The antenna 170, the controller 150, the power supply 140, and the voltage sensor 160 can all be situated on the embedded substrate 130. Because the eye-mountable device 110 includes electronics and is configured to be contact-mounted to an eye, it is also referred to herein as an ophthalmic electronics platform.

To facilitate contact-mounting, the polymeric material 120 can have a concave surface configured to adhere (“mount”) to a moistened corneal surface (e.g., by capillary forces with a tear film coating the corneal surface). Additionally or alternatively, the eye-mountable device 110 can be adhered by a vacuum force between the corneal surface and the polymeric material due to the concave curvature. While mounted with the concave surface against the eye, the outward-facing surface of the polymeric material 120 can have a convex curvature that is formed to not interfere with eye-lid motion while the eye-mountable device 110 is mounted to the eye. For example, the polymeric material 120 can be a substantially transparent curved polymeric disk shaped similarly to a contact lens.

The polymeric material 120 can include one or more biocompatible materials, such as those employed for use in contact lenses or other ophthalmic applications involving direct contact with the corneal surface. The polymeric material 120 can optionally be formed in part from such biocompatible materials or can include an outer coating with such biocompatible materials. The polymeric material 120 can include materials configured to moisturize the corneal surface, such as hydrogels and the like. In some embodiments, the polymeric material 120 can be a deformable (“non-rigid”) material to enhance wearer comfort. In some embodiments, the polymeric material 120 can be shaped to provide a predetermined, vision-correcting optical power, such as can be provided by a contact lens.

The substrate 130 includes one or more surfaces suitable for mounting the voltage sensor 160, the controller 150, the power supply 140, and the antenna 170. The substrate 130 can be employed both as a mounting platform for chip-based circuitry (e.g., by flip-chip mounting to connection pads) and/or as a platform for patterning conductive materials (e.g., gold, platinum, palladium, titanium, copper, aluminum, silver, metals, other conductive materials, combinations of these, etc.) to create electrodes, interconnects, connection pads, antennae, etc. In some embodiments, substantially transparent conductive materials (e.g., indium tin oxide) can be patterned on the substrate 130 to form circuitry, electrodes, etc. For example, the antenna 170 can be formed by forming a pattern of gold or another conductive material on the substrate 130 by deposition, photolithography, electroplating, etc. Similarly, interconnects 151, 157 between the controller 150 and the voltage sensor 160, and between the controller 150 and the antenna 170, respectively, can be formed by depositing suitable patterns of conductive materials on the substrate 130. A combination of microfabrication techniques including, without limitation, the use of photoresists, masks, deposition techniques, and/or plating techniques can be employed to pattern materials on the substrate 130. The substrate 130 can be a relatively rigid material, such as polyethylene terephthalate (“PET”) or another material configured to structurally support the circuitry and/or chip-based electronics within the polymeric material 120. The eye-mountable device 110 can alternatively be arranged with a group of unconnected substrates rather than a single substrate. For example, the controller 150 and a voltage sensor 160 can be mounted to one substrate, while the antenna 170 is mounted to another substrate and the two can be electrically connected via the interconnects 157.

In some embodiments, the voltage sensor 160 (and the substrate 130) can be positioned away from the center of the eye-mountable device 110 and thereby avoid interference with light transmission to the central, light-sensitive region of the eye. For example, where the eye-mountable device 110 is shaped as a concave-curved disk, the substrate 130 can be embedded around the periphery (e.g., near the outer circumference) of the disk. In some embodiments, however, the voltage sensor 160 (and the substrate 130) can be positioned in or near the central region of the eye-mountable device 110. Additionally or alternatively, the voltage sensor 160 and/or substrate 130 can be substantially transparent to incoming visible light to mitigate interference with light transmission to the eye. Moreover, in some embodiments, the voltage sensor 160 can include a pixel array (not shown) that emits and/or transmits light to be received by the eye according to display instructions. Thus, the voltage sensor 160 can optionally be positioned in the center of the eye-mountable device so as to generate perceivable visual cues to a wearer of the eye-mountable device 110, such as by displaying information (e.g., characters, symbols, flashing patterns, etc.) on the pixel array.

The substrate 130 can be ring-shaped with a radial width dimension sufficient to provide a mounting platform for the embedded electronics components. The substrate 130 can have a thickness sufficiently small to allow the substrate 130 to be embedded in the polymeric material 120 without influencing the profile of the eye-mountable device 110. The substrate 130 can have a thickness sufficiently large to provide structural stability suitable for supporting the electronics mounted thereon. For example, the substrate 130 can be shaped as a ring with a diameter of about 10 millimeters, a radial width of about 1 millimeter (e.g., an outer radius 1 millimeter larger than an inner radius), and a thickness of about 50 micrometers. The substrate 130 can optionally be aligned with the curvature of the eye-mounting surface of the eye-mountable device 110 (e.g., convex surface). For example, the substrate 130 can be shaped along the surface of an imaginary cone between two circular segments that define an inner radius and an outer radius. In such an example, the surface of the substrate 130 along the surface of the imaginary cone defines an inclined surface that is approximately aligned with the curvature of the eye mounting surface at that radius.

The power supply 140 is configured to harvest ambient energy to power the controller 150 and voltage sensor 160. For example, a radio-frequency energy-harvesting antenna 142 can capture energy from incident radio radiation. Additionally or alternatively, solar cell(s) 144 (“photovoltaic cells”) can capture energy from incoming ultraviolet, visible, and/or infrared radiation. Furthermore, an inertial power scavenging system can be included to capture energy from ambient vibrations. The energy harvesting antenna 142 can optionally be a dual-purpose antenna that is also used to communicate information to the reader 180. That is, the functions of the communication antenna 170 and the energy harvesting antenna 142 can be accomplished with the same physical antenna.

A rectifier/regulator 146 can be used to condition the captured energy to a stable DC supply voltage 141 that is supplied to the controller 150. For example, the energy harvesting antenna 142 can receive incident radio frequency radiation. Varying electrical signals on the leads of the antenna 142 are output to the rectifier/regulator 146. The rectifier/regulator 146 rectifies the varying electrical signals to a DC voltage and regulates the rectified DC voltage to a level suitable for operating the controller 150. Additionally or alternatively, output voltage from the solar cell(s) 144 can be regulated to a level suitable for operating the controller 150. The rectifier/regulator 146 can include one or more energy storage devices to mitigate high frequency variations in the ambient energy gathering antenna 142 and/or solar cell(s) 144. For example, one or more energy storage devices (e.g., a capacitor, an inductor, etc.) can be connected in parallel across the outputs of the rectifier 146 to regulate the DC supply voltage 141 and configured to function as a low-pass filter.

The controller 150 is turned on when the DC supply voltage 141 is provided to the controller 150, and the logic in the controller 150 operates the voltage sensor 160 and the antenna 170. The controller 150 can include logic circuitry configured to operate the voltage sensor 160 so as to interact with the antenna 170 to control the impedance of the antenna 170. The impedance of the antenna 170 may be used to communicate via backscatter radiation. Antenna 170 and backscatter radiation are discussed further below.

In one example, the controller 150 includes a sensor interface module 152 that is configured to interface with the voltage sensor 160. The voltage sensor 160 can be, for example, an electrical sensor configured to provide an output based on an input voltage of the voltage sensor 160. A voltage can be applied at the input of the voltage sensor 160. The voltage sensor 160 may responsively create an output based on the input voltage. However, in some instances the input voltage may not be sufficiently high to power the voltage sensor 160. When the input voltage is not high enough to power the voltage sensor 160, the voltage sensor 160 may not provide any output. Although the current disclosure generally referrers to voltage sensor 160 as sensing a voltage, various other electrical sensors may be used in the place of voltage sensor 160. For example, a current sensor, a power sensor, or other electrical sensor may be used in the place of the voltage sensor 160 within the context of the present disclosure.

The controller 150 can optionally include a display driver module 154 for operating a pixel array. The pixel array can be an array of separately programmable light transmitting, light reflecting, and/or light emitting pixels arranged in rows and columns. The individual pixel circuits can optionally include liquid crystal technologies, microelectromechanical technologies, emissive diode technologies, etc. to selectively transmit, reflect, and/or emit light according to information from the display driver module 154. Such a pixel array can also optionally include more than one color of pixels (e.g., red, green, and blue pixels) to render visual content in color. The display driver module 154 can include, for example, one or more data lines providing programming information to the separately programmed pixels in the pixel array and one or more addressing lines for setting groups of pixels to receive such programming information. Such a pixel array situated on the eye can also include one or more lenses to direct light from the pixel array to a focal plane perceivable by the eye.

The controller 150 can also include a communication circuit 156 for sending and/or receiving information via the antenna 170. The communication circuit 156 can optionally include one or more oscillators, mixers, frequency injectors, etc. to modulate and/or demodulate information on a carrier frequency to be transmitted and/or received by the antenna 170. As previously stated, in some examples, the eye-mountable device 110 is configured to indicate an output from a voltage sensor 160 by modulating an impedance of the antenna 170 in a manner that is perceivable by the reader 180. For example, the communication circuit 156 can cause variations in the amplitude, phase, and/or frequency of backscatter radiation from the antenna 170, and such variations can be detected by the reader 180.

The controller 150 is connected to the voltage sensor 160 via interconnects 151. For example, where the controller 150 includes logic elements implemented in an integrated circuit to form the sensor interface module 152 and/or display driver module 154, a patterned conductive material (e.g., gold, platinum, palladium, titanium, copper, aluminum, silver, metals, combinations of these, etc.) can connect a terminal on the chip to the voltage sensor 160. Similarly, the controller 150 is connected to the antenna 170 via interconnects 157.

It is noted that the block diagram shown in FIG. 1 is described in connection with functional modules for convenience in description. However, embodiments of the eye-mountable device 110 can be arranged with one or more of the functional modules (“sub-systems”) implemented in a single chip, integrated circuit, and/or physical component. For example, while the rectifier/regulator 146 is illustrated in the power supply block 140, the rectifier/regulator 146 can be implemented in a chip that also includes the logic elements of the controller 150 and/or other features of the embedded electronics in the eye-mountable device 110. Thus, the DC supply voltage 141 that is provided to the controller 150 from the power supply 140 can be a supply voltage that is provided to components on a chip by rectifier and/or regulator components located on the same chip. That is, the functional blocks in FIG. 1 shown as the power supply block 140 and controller block 150 need not be implemented as physically separated modules. Moreover, one or more of the functional modules described in FIG. 1 can be implemented by separately packaged chips electrically connected to one another.

Additionally or alternatively, the energy harvesting antenna 142 and the communication antenna 170 can be implemented with the same physical antenna. For example, a loop antenna can both harvest incident radiation for power generation and communicate information via backscatter radiation.

The reader 180 can be configured to be external to the eye; i.e., is not part of the eye-mountable device. Reader 180 can include one or more antennas 188 to send and receive wireless signals 171 to and from the eye-mountable device 110. In some embodiments, reader 180 can communicate using hardware and/or software operating according to one or more standards, such as, but not limited to, a RFID standard, a Bluetooth standard, a Wi-Fi standard, a Zigbee standard, etc.

Reader 180 can also include a computing system with a processor 186 in communication with a memory 182. Memory 182 is a non-transitory computer-readable medium that can include, without limitation, magnetic disks, optical disks, organic memory, and/or any other volatile (e.g. RAM) or non-volatile (e.g. ROM) storage system readable by the processor 186. The memory 182 can include a data storage 183 to store indications of data, such as sensor readings (e.g., from the voltage sensor 160), program settings (e.g., to adjust behavior of the eye-mountable device 110 and/or reader 180), etc. The memory 182 can also include program instructions 184 for execution by the processor 186 to cause the reader 180 to perform processes specified by the instructions 184. For example, the program instructions 184 can cause reader 180 to provide a user interface that allows for retrieving information communicated from the eye-mountable device 110 (e.g., sensor outputs from the voltage sensor 160). The reader 180 can also include one or more hardware components for operating the antenna 188 to send and receive the wireless signals 171 to and from the eye-mountable device 110. For example, oscillators, frequency injectors, encoders, decoders, amplifiers, filters, etc. can drive the antenna 188 according to instructions from the processor 186.

In some embodiments, reader 180 can be a smart phone, digital assistant, or other portable computing device with wireless connectivity sufficient to provide the wireless communication link 171. In other embodiments, reader 180 can be implemented as an antenna module that can be plugged in to a portable computing device; e.g., in scenarios where the communication link 171 operates at carrier frequencies not commonly employed in portable computing devices. In even other embodiments discussed below in more detail in the context of at least FIG. 5, the reader 180 can be a special-purpose device configured to be worn relatively near a wearer's eye to allow the wireless communication link 171 to operate with a low power budget. For example, the reader 180 can be integrated in a piece of jewelry such as a necklace, earring, etc. or integrated in an article of clothing worn near the head, such as a hat, headband, etc.

FIG. 2A is a bottom view of an example eye-mountable electronic device 210 (or ophthalmic electronics platform). FIG. 2B is an aspect view of the example eye-mountable electronic device shown in FIG. 2A. It is noted that relative dimensions in FIGS. 2A and 2B are not necessarily to scale, but have been rendered for purposes of explanation only in describing the arrangement of the example eye-mountable electronic device 210. The eye-mountable device 210 is formed of a polymeric material 220 shaped as a curved disk. In some embodiments, eye-mountable device 210 can include some or all of the above-mentioned aspects of eye-mountable device 110. In other embodiments, eye-mountable device 110 can further include some or all of the herein-mentioned aspects of eye-mountable device 210.

The polymeric material 220 can be a substantially transparent material to allow incident light to be transmitted to the eye while the eye-mountable device 210 is mounted to the eye. The polymeric material 220 can be a biocompatible material similar to those employed to form vision correction and/or cosmetic contact lenses in optometry, such as polyethylene terephthalate (“PET”), polymethyl methacrylate (“PMMA”), polyhydroxyethylmethacrylate (“polyHEMA”), silicone hydrogels, combinations of these, etc. The polymeric material 220 can be formed with one side having a concave surface 226 suitable to fit over a corneal surface of an eye. The opposite side of the disk can have a convex surface 224 that does not interfere with eyelid motion while the eye-mountable device 210 is mounted to the eye. A circular outer side edge 228 connects the concave surface 224 and convex surface 226.

The eye-mountable device 210 can have dimensions similar to a vision correction and/or cosmetic contact lenses, such as a diameter of approximately 1 centimeter, and a thickness of about 0.1 to about 0.5 millimeters. However, the diameter and thickness values are provided for explanatory purposes only. In some embodiments, the dimensions of the eye-mountable device 210 can be selected according to the size and/or shape of the corneal surface of the wearer's eye.

The polymeric material 220 can be formed with a curved shape in a variety of ways. For example, techniques similar to those employed to form vision-correction contact lenses, such as heat molding, injection molding, spin casting, etc. can be employed to form the polymeric material 220. While the eye-mountable device 210 is mounted in an eye, the convex surface 224 faces outward to the ambient environment while the concave surface 226 faces inward, toward the corneal surface. The convex surface 224 can therefore be considered an outer, top surface of the eye-mountable device 210 whereas the concave surface 226 can be considered an inner, bottom surface. The “bottom” view shown in FIG. 2A is facing the concave surface 226. From the bottom view shown in FIG. 2A, the outer periphery 222, near the outer circumference of the curved disk is curved to extend out of the page, whereas the central region 221, near the center of the disk is curved to extend into the page.

A substrate 230 is embedded in the polymeric material 220. The substrate 230 can be embedded to be situated along the outer periphery 222 of the polymeric material 220, away from the central region 221. The substrate 230 does not interfere with vision because it is too close to the eye to be in focus and is positioned away from the central region 221 where incident light is transmitted to the eye-sensing portions of the eye. Moreover, the substrate 230 can be formed of a transparent material to further mitigate effects on visual perception.

The substrate 230 can be shaped as a flat, circular ring (e.g., a disk with a centered hole). The flat surface of the substrate 230 (e.g., along the radial width) is a platform for mounting electronics such as chips (e.g., via flip-chip mounting) and for patterning conductive materials (e.g., via microfabrication techniques such as photolithography, deposition, plating, etc.) to form electrodes, antenna(e), and/or interconnections. The substrate 230 and the polymeric material 220 can be approximately cylindrically symmetric about a common central axis. The substrate 230 can have, for example, a diameter of about 10 millimeters, a radial width of about 1 millimeter (e.g., an outer radius 1 millimeter greater than an inner radius), and a thickness of about 50 micrometers. However, these dimensions are provided for example purposes only, and in no way limit the present disclosure. The substrate 230 can be implemented in a variety of different form factors, similar to the discussion of the substrate 130 in connection with FIG. 1 above.

A loop antenna 270, controller 250, and voltage sensor 260 are disposed on the embedded substrate 230. The controller 250 can be a chip including logic elements configured to operate the voltage sensor 260 and the loop antenna 270. The controller 250 is electrically connected to the loop antenna 270 by interconnects 257 also situated on the substrate 230. Similarly, the controller 250 is electrically connected to the voltage sensor 260 by an interconnect 251. The interconnects 251, 257, the loop antenna 270, and any conductive electrodes (e.g., for a voltage sensor, etc.) can be formed from conductive materials patterned on the substrate 230 by a process for precisely patterning such materials, such as deposition, photolithography, etc. The conductive materials patterned on the substrate 230 can be, for example, gold, platinum, palladium, titanium, carbon, aluminum, copper, silver, silver-chloride, conductors formed from noble materials, metals, combinations of these, etc.

As shown in FIG. 2A, which is a view facing the convex surface 224 of the eye-mountable device 210, voltage sensor 260 is mounted to a side of the substrate 230 facing the convex surface 224. In some embodiments, some electronic components can be mounted on one side of the substrate 230, while other electronic components are mounted to the opposing side, and connections between the two can be made through conductive materials passing through the substrate 230.

The loop antenna 270 is a layer of conductive material patterned along the flat surface of the substrate to form a flat conductive ring. In some instances, the loop antenna 270 can be formed without making a complete loop. For instances, the loop antenna can have a cutout to allow room for the controller 250 and voltage sensor 260, as illustrated in FIG. 2A. However, the loop antenna 270 can also be arranged as a continuous strip of conductive material that wraps entirely around the flat surface of the substrate 230 one or more times. For example, a strip of conductive material with multiple windings can be patterned on the side of the substrate 230 opposite the controller 250 and voltage sensor 260. Interconnects between the ends of such a wound antenna (e.g., the antenna leads) can then be passed through the substrate 230 to the controller 250.

FIG. 2C is a side cross-section view of the example eye-mountable electronic device 210 while mounted to a corneal surface 22 of an eye 10. FIG. 2D is a close-in side cross-section view enhanced to show the eye-mountable device 210. It is noted that relative dimensions in FIGS. 2C and 2D are not necessarily to scale, but have been rendered for purposes of explanation only in describing the arrangement of the example eye-mountable electronic device 210. For example, the total thickness of the eye-mountable device can be about 200 micrometers, while the thickness of the tear film layers can each be about 10 micrometers, although this ratio may not be reflected in the drawings. Some aspects are exaggerated to allow for illustration and facilitate explanation.

The eye 10 includes a cornea 20 that is covered by bringing the upper eyelid 30 and lower eyelid 32 together over the top of the eye 10. Incident light is received by the eye 10 through the cornea 20, where light is optically directed to light sensing elements of the eye 10 (e.g., rods and cones, etc.) to stimulate visual perception. The motion of the eyelids 30, 32 distributes a tear film across the exposed corneal surface 22 of the eye 10. The tear film is an aqueous solution secreted by the lacrimal gland to protect and lubricate the eye 10. When the eye-mountable device 210 is mounted in the eye 10, a tear film coats both the concave and convex surfaces 224, 226 with an inner layer (along the concave surface 226) and an outer layer (along the convex layer 224). The tear film layers can be about 10 micrometers in thickness and together account for about 10 microliters.

The tear film layers are distributed across the corneal surface 22 and/or the convex surface 224 by motion of the eyelids 30, 32. For example, the eyelids 30, 32 raise and lower, respectively, to spread a small volume of tear film across the corneal surface 22 and/or the convex surface 224 of the eye-mountable device 210. The tear film layer on the corneal surface 22 also facilitates mounting the eye-mountable device 210 by capillary forces between the concave surface 226 and the corneal surface 22. In some embodiments, the eye-mountable device 210 can also be held over the eye in part by vacuum forces against corneal surface 22 due to the concave curvature of the eye-facing concave surface 226.

As shown in the cross-sectional views in FIGS. 2C and 2D, the substrate 230 can be inclined such that the flat mounting surfaces of the substrate 230 are approximately parallel to the adjacent portion of the convex surface 224. As described above, the substrate 230 is a flattened ring with an inward-facing surface 232 (facing concave surface 226 of the polymeric material 220) and an outward-facing surface 234 (facing convex surface 224). The substrate 230 can have electronic components and/or patterned conductive materials mounted to either or both mounting surfaces 232, 234. As shown in FIG. 2D, the voltage sensor 260, controller 250, and conductive interconnect 251 may be mounted on the outward-facing surface 234. However, in other embodiments, the various components may also be mounted on the inward-facing surface.

The polymer layer defining the anterior side may be greater than 50 micrometers thick, whereas the polymer layer defining the posterior side may be less than 150 micrometers. Thus, voltage sensor 260 may be at least 50 micrometers away from the convex surface 224 and may be a greater distance away from the concave surface 226. However, in other examples, the voltage sensor 260 may be mounted on the inward-facing surface 232 of the substrate 230 such that the voltage sensor 260 are facing concave surface 226. The voltage sensor 260 could also be positioned closer to the concave surface 226 than the convex surface 224.

FIG. 3 is a functional block diagram of a system 300 for adjusting the power of an external reader. The system 300 includes an eye-mountable device 210 with embedded electronic components in communication with and powered by reader 180. Reader 180 can also be configured to communicate with a display device (the display device may or may not be integrated with the reader 180 as UI 348). Reader 180 and eye-mountable device 210 can communicate according to one communication protocol or standard, shown in FIG. 3 as RF Power 341. In one particular embodiment, the protocol used for RF Power 341 and Backscatter communication 343 is an RFID protocol. The eye-mountable device 210 includes an antenna 312 for capturing radio frequency (RF) power 341 from the reader 180. The antenna 312 may also create backscatter communication 343.

The eye-mountable device 210 includes rectifier 314, energy storage 316 (that may output unregulated voltage 317), and regulator 318 for generating regulated supply voltages 330, 332 to operate the embedded electronics. The eye-mountable device 210 includes a voltage sensor 321 that may have a sensor interface 320. The eye-mountable device 210 includes hardware logic 324 for communicating results from the sensor 321 to the reader 180 by modulating the impedance of the antenna 312. An impedance modulator 325 (shown symbolically as a switch in FIG. 3) can be used to modulate the antenna impedance according to instructions from the hardware logic 324. Similar to the eye-mountable device 110 discussed above in connection with FIG. 1, the eye-mountable device 210 can include a mounting substrate embedded within a polymeric material configured to be mounted to an eye.

With reference to FIG. 3, in various embodiments, the voltage sensor 321 measures either the unregulated voltage 317 or the regulated supply voltage 332. In various embodiments, the voltage measured by the voltage sensor 321 may come from different sources. As shown in FIG. 3, the regulator 318 may provide the regulated supply voltage 332 and the energy storage 316 may provide unregulated voltage 317. However, in other embodiments, only one of the regulated supply voltage 332 and the unregulated voltage 317 may be provided to the voltage sensor 321. In additional embodiments, the regulated supply voltage 332 provided to the voltage sensor 321 may be the same regulated supply voltage 330 that supplies power to the hardware logic 324. The connections shown in FIG. 3 are one example of possible configurations for the voltage sensor 321. The sensor interface 320 may be configured as a part of the voltage sensor 321 itself. For example, the sensor interface 320 may convert the output of the voltage sensor 321 into a format that in understandable by the hardware logic 324.

In other embodiments, the sensor interface 320 can contain an electrical sensor other than voltage sensor 321. For example, a current sensor, a power sensor, or other electrical sensor may be used in the place of the voltage sensor 321 within the context of the present disclosure. The connections to the sensor interface 320 may change depending on the specific type of sensor that forms a portion of sensor interface 320. For example, the sensor unit 320 contains a parallel electrical connection to the hardware logic 324. A current sensor may be placed in a series electrical connection with one of the hardware logic 324, voltage regulator 318, or other component.

The rectifier 314, energy storage 316, and voltage regulator 318 operate to harvest energy from received RF power 341. RF power 341 causes radio frequency electrical signals on leads of the antenna 312. The rectifier 314 is connected to the antenna leads and converts the radio frequency electrical signals to a DC voltage. The energy storage 316 (e.g., capacitor) is connected across the output of the rectifier 314 to filter out high frequency components of the DC voltage. The regulator 318 receives the filtered DC voltage (e.g. unregulated voltage 317) and outputs both a regulated supply voltage 330 to operate the hardware logic 324 and a regulated supply voltage 332 to operate the voltage sensor 321 of the sensor interface 320. For example, the supply voltage can be equivalent to the voltage of the energy storage 316. In another example, the supply voltage can be equivalent to the voltage of the rectified DC voltage from the rectifier 314. Additionally, the regulated supply voltage 330 can be a voltage suitable for driving digital logic circuitry, such as approximately 1.2 volts, approximately 3 volts, etc. The voltage needed as the regulated supply voltage 330 may change depending on a functionality requirement of the logic 324 (or a voltage requirement of other components of the eye-mountable device 210). Reception of the RF power 341 from the reader 180 (or another source, such as ambient radiation, etc.) causes the regulated supply voltages 330, 332 to be supplied to the sensor 320 and hardware logic 324. While powered, the sensor 320 and hardware logic 324 are configured to generate and measure a voltage (such as either unregulated voltage 317 or regulated supply voltages 332) and communicate the results.

The sensor results can be communicated back to the reader 180 via backscatter radiation 343 from the antenna 312. The hardware logic 324 receives the supply voltage from the sensor interface 320 (or the voltage sensor 321 itself) and modulates (325) the impedance of the antenna 312 in accordance with the supply voltage measured by the sensor 320. The antenna impedance and/or change in antenna impedance are detected by the reader 180 via the backscatter signal 343.

Reader 180 can include an antenna and RF front end 342 and logic components 344 to communicate using a radio protocol, decode the information indicated by the backscatter signal 343, provide digital inputs to a processing system 346 and receive inputs and/or provide outputs via user interface 348. The radio protocol can be, for example, an RFID protocol. In some embodiments, part or all of eye-mountable device 210 can be configured to perform some or all features of an RFID tag. For example, as shown in FIG. 3, some or all of the components shown as tag 370 of eye-mountable device 210 can perform some or all features of an RFID tag; e.g., antenna 312, rectifier 314, energy storage 316, voltage regulator 318, hardware logic 324, etc.

In some embodiments, one or more of the features shown as separate functional blocks can be implemented (“packaged”) on a single chip. For example, the eye-mountable device 210 can be implemented with the rectifier 314, energy storage 316, voltage regulator 318, sensor interface 320, and the hardware logic 324 packaged together in a single chip or controller module. Such a controller can have interconnects (“leads”) connected to the loop antenna 312 and the sensor electrodes 322, 323. Such a controller operates to harvest energy received at the loop antenna 312, measure the supply voltage created by the harvested energy, and indicate the measured supply voltage via the antenna 312 (e.g., through the backscatter communication 343).

A processing system, such as, but not limited to, processing system 346 or processing system 356, can include one or more processors and one or more storage components. Example processor(s) include, but are not limited to, CPUs, Graphics Processing Units (GPUs), digital signal processors (DSPs), application specific integrated circuits (ASICs). Example storage component(s) include, but are not limited to volatile and/or non-volatile storage components, e.g., optical, magnetic, organic or other memory, disc storage; Random Access Memory (RAM), Read-Only Memory (ROM), flash memory, optical memory unit, and disc memory. The storage component(s) can be configured to store software and data; e.g., computer-readable instructions configured, when executed by a processor of the processing system, to cause the processing system to carry out functions such as but not limited to the herein-described functions of reader 180, eye-mountable device 210, and/or display device 350.

The reader 180 can associate the backscatter signal 343 with the sensor result (e.g., via the processing system 346 according to a pre-programmed relationship associating impedance of the antenna 312 with output from the sensor 320). The processing system 346 can then store the indicated sensor results (e.g., induced supply voltage) in a local memory and/or an external memory (e.g., by communicating with the external memory either on display device 350 or through a network).

User interface 348 of reader 180 can include an indicator, such as but not limited to one or more light-emitting diodes (LEDs) and/or speakers, that can indicate that reader 180 is operating and provide some information about its status. For example, reader 180 can be configured with an LED that displays one color (e.g., green) when operating normally and another color (e.g., red) when operating abnormally. In other embodiments, the LED(s) can change display when processing and/or communicating data in comparison to when idle (e.g., periodically turn on and off while processing data, constantly stay on or constantly stay off while idle). The reader 180 may also provide an audio output based on the voltage sensor data.

In some embodiments, one or more of the LED(s) of user interface 348 can indicate a status of sensor data; e.g., not display when sensor data are either within normal range(s) or unavailable, display in a first color when sensor data are either outside normal range(s) but not extremely high or low, and display a second color when the sensor data are extremely high and/or low. For example, if the voltage sensor data is unavailable, it may indicate that the RF Power 341 is too low to induce a voltage in the eye-mountable device 210 to power the voltage sensor 321. In another embodiment, the voltage sensor data may indicate the voltage is too low based on the RF Power 341 being too low to induce a voltage to power a component (or a function) of the eye-mountable device 210. In yet another embodiment, the voltage sensor data may indicate the voltage is too high based on the RF Power 341 being high enough to induce a voltage power a component (or a function) of the eye-mountable device 210, but the voltage is sufficiently higher than needed. In some embodiments, the processing system 346 may responsively adjust the RF Power 341 based on the voltage sensor data.

In some embodiments, reader 180 can communicate with devices in addition to eye-mountable device 210/tag 370. For example, the reader 180 may also function as a cellular phone or other mobile device.

FIG. 4 is a block diagram of a system 400 with eye-mountable device 210 operated by a reader 180 to obtain a series of supply voltage measurements over time. An electrical sensor; e.g., an embodiment of sensor 321, can be included with eye-mountable device 210. As shown in FIG. 4, eye-mountable device 210 is configured to be contact-mounted over a corneal surface of an eye 10. The ophthalmic electrical sensor can be operated to be transitioned into an active measurement mode in response to receiving a signal from the reader 180.

The reader 180 includes a processing system 346, configured with memory 414.

The processing system 412 can be a computing system that executes computer-readable instruction stored in the memory 414 to cause the reader 180/system 400 to obtain a time series of measurements by intermittently transmitting a measurement signal to eye-mountable device 210. In response to the measurement signal, one or more sensors of eye-mountable device 210; e.g., electrical sensor 430, can take measurement(s), obtain results of the measurement(s), and communicate the results to reader 180 via backscatter 422. As discussed above regarding FIG. 3, reader 180 can provide RF power, such as RF power 420, to be harvested by the eye-mountable device 210. For example, impedance of an antenna of eye-mountable device 210 can be modulated in accordance with the sensor result such that the backscatter radiation 422 indicates the sensor results. Reader 180 can also use memory 414 to store indications of supply voltage measurements communicated by the voltage sensor 430. The reader 180 can thus be operated to intermittently power the electrical sensor 430 so as to obtain a time series of supply voltage measurements.

FIG. 5 shows an example wearer 500 wearing two eye-mountable devices 210 a, 210 b, a band 522, earrings 524 a, 524 b, and a necklace 526. As discussed above at least in the context of FIGS. 3, 4A, and 4B, each eye-mountable device 210 a, 210 b can be configured with sensor(s) to measure at least the supply voltage induced in the respective lens.

The functionality of band 522 can be performed by a structure of another device, e.g., an eye-glass frame, a head-mountable computer frame, a cap, a hat, part of a hat or cap (e.g., a hat band or bill of a baseball cap), a headphone headband, etc., or by a separate band; e.g., a head band, a scarf or bandanna worn as a head band. For examples, band 522 can be supported by ear(s), nose, hair, skin, and/or a head of wearer 500, and perhaps by external devices e.g., stick pins, bobby pins, headband elastics, snaps. Other and different support(s) for band 522 are possible as well.

One or more of band 522, earrings 524 a, 524 b, and necklace 526 can be configured to include one or more readers; e.g., the above-mentioned reader 180. FIG. 5 shows three example positions 180 a, 180 b, and 180 c for readers in band 522. For example, if only eye-mountable device 210 a has a sensor, then a reader, such as reader 180, can be mounted in example positions 180 a and/or 180 b to send commands and power to eye-mountable device 210 a. Similarly, to power and communicate with a sensor in eye-mountable device 210 b, a reader mounted in band 522, such as reader 180, can be mounted in example positions 180 b and/or 180 c.

Each of or both earrings 524 a, 524 b can be configured with respective readers 180 d, 180 e for communicating with and power sensors in respective eye-mountable devices 210 a, 210 b. Necklace 526 can be configured with one or more readers 180 f, 180 g, 180 h for communicating with and power sensors in respective eye-mountable device 210 a, 210 b. Other embodiments are possible as well; e.g., readers in positions 180 a-180 c or near those positions can be configured as part of a hat, headband, scarf, jewelry (e.g., a brooch), glasses, head mounted device, and/or other apparatus.

In some embodiments, a reader can power a sensor in eye-mountable device 210 using a low-power transmission; e.g., a transmission of 1 watt or less of power. In these embodiments, the reader can be within a predetermined distance; e.g., 1 foot, 40 cm, of eye-mountable device 210 a, 210 b to power the sensor.

FIG. 6 shows a scenario 600 where reader 180 communicates with an eye-mountable device (EMD) 210. In scenario 600, eye-mountable device 210 and reader 180 communicate using an RFID protocol; e.g., an RFID Generation 2 protocol such as specified in “EPC™ Radio-Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz-960 MHz, Version 1.2.0”, Oct. 23, 2008, EPCglobal Inc.

In other scenarios, the reader, tag, display device, and/or other device(s) can communicate using different and/or additional protocols; e.g., an IEEE 802.11 protocol (“Wi-Fi”), an IEEE 802.15 protocol (“Zigbee”), a Local Area Network (LAN) protocol, a Wireless Wide Area Network (WWAN) protocol such as but not limited to a 2G protocol (e.g., CDMA, TDMA, GSM), a 3G protocol (e.g., CDMA-2000, UMTS), a 4G protocol (e.g., LTE, WiMAX), a wired protocol (e.g., USB, a wired IEEE 802 protocol, RS-232, DTMF, dial pulse). Many other examples of protocol(s) and combination(s) of protocols can be used as well.

Although scenario 600 in shown in a linear order, the blocks may also be performed in a different order. Additionally, in some embodiments, at least one block of scenario 600 may be performed in parallel to another block of scenario 600.

Scenario 600 begins with reader 180 sending communication to the eye-mountable device (EMD) 210 with a transmit RF Power 620. The transmitted RF Power 620 may be a radio signal with a defined radio power. In some embodiments, the radio power may be transmitted as a continuous wave (CW) radio signal or the radio power may be transmitted as a pulse-modulated radio signal. In other embodiments, the RF Power 620 transmission may take a form other than a CW or pulse-modulated radio signal. In some embodiments, the communication may be an initialization of the eye-mountable device 210. However, in other embodiments, the communication may be the normal operation of the eye-mountable device 210.

When the EMD 210 received the RF power 620, it converts the RF power 620 into a supply voltage. The supply voltage is used to power various components within the EMD 210. The EMD 210 may also be configured to measure the supply voltage created in the EMD 210. The EMD 210 may include an electrical component configured to measure the supply voltage induced in the EMD 210 from the RF power 620. Additionally, the EMD 210 may be configured to create a backscatter signal based on the measured supply voltage 622.

After transmitting RF Power 620 to an EMD 210, the reader 180 may responsively receive a Supply Voltage Indication 624 communicated from the EMD 210. The EMD may communicate the Supply Voltage Indication 624 through backscatter radiation of the RF Power 620. The backscatter radiation may be created by a modulation of an impedance of an antenna of the EMD 210. The EMD 210 may be configured to modulate the antenna impedance to create a signal to communicate a supply voltage induced in the EMD 210 by RF Power 620.

Once the Reader 180 receives the Supply Voltage Indication 624, it may Analyze the Voltage Indication 626. When the Reader 180 Analyzes the Voltage Indication 626, it may determine a supply voltage that was induced in the EMD 210 by the RF power 620. In some embodiments, Analyzing the Voltage Indication 626 may determine that a signal received as Supply Voltage Indication 624 does not actually contain an indication of supply voltage. In this instance, the lack of an indication of a supply voltage may indicate to the Reader 180 that the there is an error in the EMD 210.

Once the Reader 180 Analyzes the Voltage Indication 626, it may responsively Determine a Voltage Requirement 628. The Reader 180 may Determine a Voltage Requirement 628. The Reader 180 may determine a voltage requirement in several ways. First, the Reader may determine a desired function for the EMD 210. Each desired function may have an associated voltage requirement. The Reader 180 may compare the voltage requirement for the desired function of the EMD 210 (or, in an instance where the EMD 210 performs multiple functions, the highest voltage requirement needed for any function). Once the Reader 180 Determines a Voltage Requirement 628, the Reader 180 may compare the voltage requirement with the voltage indication to determine a difference between the Determined Voltage Requirement 626 and the Voltage Indication 626. In other embodiments, the Reader 180 may not have been able to determine an inducted voltage in the EMD 210 when Analyzing the Voltage Indication 626. In this embodiment, the Reader 180 may determine that the voltage induced in the EMD 210 is too low to power the voltage sensor.

Once the reader has Determined Voltage Requirement 628 (or determined the induced voltage is too low), the reader may transmit to the EMD 120 with an Adjusted RF Power 630. If the Determined Voltage Requirement 628 is greater than the induced voltage determined by Determined Voltage Requirement 628, then the Adjusted RF Power 628 will be increased compared to the RF Power 620. If the Determined Voltage Requirement 628 is less than the induced voltage determined by Determined Voltage Requirement 628, then the Adjusted RF Power 630 may be decreased compared to the RF Power 620. The Adjusted RF Power 630 does not have to be decreased in order to power various components of the EMD 210 (as the voltage is already sufficiently high), but the Adjusted RF Power 630 may be lowered to both conserve power of the Reader 180 and reduce the amount of RF Power coupled into the body of the person wearing the EMD 210. If the Reader 180 determines that the voltage induced in the EMD 210 is too low to power the voltage sensor, the Reader 180 may increase the RF Power when transmitting the Adjusted RF Power 630. Scenario 600 may be repeated after the RF Power is adjusted. Other examples of scenario 600 are possible as well.

FIG. 7 is a flow chart of an example method 700. Method 700 can be carried out by a device, such as a tag in an eye-mountable device, or a device that includes a processor, such the hardware logic 324, the hardware logic may include a computer readable medium storing machine-readable instructions, where the machine-readable instructions, when executed by a processing component of the device, are configured to cause the device to carry out some or all of the techniques described herein as method 700.

Method 700 can begin at block 710. At block 710, the tag can receive RF (i.e. electromagnetic) power, such as discussed above in the context of at least FIG. 6. An antenna in the tag may receive the RF power and output an RF signal (as a voltage). The RF signal may be proportional to the received RF power. The tag can be part of an eye-mountable device; e.g., tag 370 of eye-mountable device 210, such as discussed above in more detail in the context of at least FIG. 3. In some embodiments, the reader can be within a predetermined distance from the tag when transmitting RF power to the tag, such as discussed above in the context of at least FIG. 5. In other embodiments, the reader can be part of an HMD, such as discussed above in the context of at least FIG. 5.

At block 720, the tag can rectify the RF signal output from the antenna. By rectifying the supply signal, a direct current (DC) supply voltage may be created. Because the supply signal may be a conversion of the propagating RF power to a guided electric RF signal, it may have alternating current properties. For example, the amplitude of the supply signal may vary from a positive voltage to a negative voltage. After rectification, the supply voltage does not have an amplitude that swings from positive to negative. Therefore the supply voltage may be considered an unregulated DC supply voltage.

Additionally, the rectified supply voltage may also be applied across a capacitor or other electrical storage component. The capacitor (or storage component) may perform at least one of two functions. First, the capacitor may store some electrical energy. This electrical energy may be used to power components of the tag if the RF power is no longer applied to the antenna of the tag. Second, the capacitor may also provide some smoothing (e.g. low-pass filtering) of the rectified voltage. This smoothing may allow a more consistent supply voltage to be supplied to the various components of the tag.

At block 730, the tag may measure the supply voltage with a measurement unit, such as a voltage sensor. The voltage sensor may be configured to use both the supply power to power itself, as well as measure the voltage of the supply voltage. In other embodiments, the tag can contain an electrical sensor other than a voltage sensor. For example, a current sensor, a power sensor, or other electrical sensor may be used in the place of the voltage sensor within the context of the present disclosure. If the electronic unit has a sensor other than a voltage sensor, a different electrical property of the supply voltage may be measured.

In some embodiments, the supply voltage measured by the voltage sensor is an unregulated voltage. The unregulated voltage may be provided by the output of the capacitor (or other energy storage device). In other embodiments, the supply voltage the voltage sensor may measure is a regulated voltage. The regulated voltage may be a voltage that comes out of a regulator component. A regulated voltage may have a more consistent and stable voltage than the unregulated voltage. Additionally, regulated voltage may be used to supply power to various components of the device.

At block 740, the tag may adjust an antenna impedance based on the measured supply voltage. The antenna impedance may be adjusted in a way to cause a backscatter signal of the RF power. The backscatter signal may communicate the measured voltage back to a reader device. Therefore, through the impedance adjustment, the tag may communicate the measured supply voltage back to the reader.

The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims.

The above detailed description describes various features and functions of the disclosed systems, devices, and methods with reference to the accompanying figures. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The example embodiments described herein and in the figures are not meant to be limiting. Other embodiments can be utilized, and other changes can be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.

With respect to any or all of the ladder diagrams, scenarios, and flow charts in the figures and as discussed herein, each block and/or communication may represent a processing of information and/or a transmission of information in accordance with example embodiments. Alternative embodiments are included within the scope of these example embodiments. In these alternative embodiments, for example, functions described as blocks, transmissions, communications, requests, responses, and/or messages may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order, depending on the functionality involved. Further, more or fewer blocks and/or functions may be used with any of the ladder diagrams, scenarios, and flow charts discussed herein, and these ladder diagrams, scenarios, and flow charts may be combined with one another, in part or in whole.

A block that represents a processing of information may correspond to circuitry that can be configured to perform the specific logical functions of a herein-described method or technique. Alternatively or additionally, a block that represents a processing of information may correspond to a module, a segment, or a portion of program code (including related data). The program code may include one or more instructions executable by a processor for implementing specific logical functions or actions in the method or technique. The program code and/or related data may be stored on any type of computer readable medium such as a storage device including a disk or hard drive or other storage medium.

The computer readable medium may also include non-transitory computer readable media such as computer-readable media that stores data for short periods of time like register memory, processor cache, and random access memory (RAM). The computer readable media may also include non-transitory computer readable media that stores program code and/or data for longer periods of time, such as secondary or persistent long term storage, like read only memory (ROM), optical or magnetic disks, compact-disc read only memory (CD-ROM), for example. The computer readable media may also be any other volatile or non-volatile storage systems. A computer readable medium may be considered a computer readable storage medium, for example, or a tangible storage device.

Moreover, a block that represents one or more information transmissions may correspond to information transmissions between software and/or hardware modules in the same physical device. However, other information transmissions may be between software modules and/or hardware modules in different physical devices.

The particular arrangements shown in the figures should not be viewed as limiting. It should be understood that other embodiments can include more or less of each element shown in a given figure. Further, some of the illustrated elements can be combined or omitted. Yet further, an example embodiment can include elements that are not illustrated in the figures.

It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art.

Example methods and systems are described above. It should be understood that the words “example” and “exemplary” are used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as being an “example” or “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or features. Reference is made herein to the accompanying figures, which form a part thereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 

What is claimed is:
 1. An apparatus comprising: an antenna configured to: receive electromagnetic radiation to form a supply signal, output a backscatter signal based on the received electromagnetic radiation, and adjust an antenna impedance to cause the backscatter of the received electromagnetic radiation; a rectifier configured to rectify the supply signal into a supply voltage; a measurement unit configured to measure the supply voltage; and a control unit configured to cause the antenna impedance to communicate the measured supply voltage via the backscatter of received electromagnetic radiation.
 2. The apparatus according to claim 1, wherein the supply voltage provides power to the components of the apparatus.
 3. The apparatus according to claim 1, wherein the control unit is further configured to determine a voltage requirement threshold.
 4. The apparatus according to claim 3, wherein the voltage requirement threshold is based on a function performed by the apparatus.
 5. The apparatus according to claim 1, wherein the supply voltage is greater than or equal to a threshold voltage of the power unit.
 6. The apparatus according to claim 1, wherein the apparatus comprises an eye-mountable device.
 7. A reader apparatus comprising: an antenna configured to: transmit electromagnetic radiation with a power level, and receive backscatter electromagnetic radiation and output a voltage-indication signal based on the backscatter electromagnetic radiation; a control unit configured to: analyze the voltage-indication signal to determine a voltage of a device that caused the backscatter electromagnetic radiation; determine a voltage requirement for the device; and responsively adjust the power level based on the voltage requirement.
 8. The reader apparatus according to claim 7, wherein the control unit determines the voltage requirement based on a threshold power requirement for the device.
 9. The reader apparatus according to claim 7, wherein the control unit determines the voltage requirement based on a function the device will perform.
 10. The reader apparatus according to claim 7, wherein the control unit is further configured to responsively adjust the power level based on both the voltage requirement and a power usage of the reader apparatus.
 11. The reader apparatus according to claim 7, wherein the control unit is further configured to responsively increase the power level based on not receiving backscatter.
 12. The reader apparatus according to claim 7, wherein the control unit is further configured to responsively increase the power level based on analyzing the voltage-indication signal to determine the voltage of the device is not high enough to power a power unit of the device.
 13. The reader apparatus according to claim 7, further comprising a speaker, wherein the speaker is configured to output a sound based on the voltage-indication signal.
 14. An method comprising: receiving electromagnetic radiation with an antenna to form a supply signal; rectifying the supply signal into a supply voltage; measuring the supply voltage with a measurement unit; and adjusting an antenna impedance based on the measured supply voltage to cause a backscatter of the received electromagnetic radiation based on both the received electromagnetic radiation and the antenna impedance.
 15. The method according to claim 14, further comprising powering components of an apparatus with the supply voltage.
 16. The method according to claim 14, further comprising determining a voltage requirement threshold.
 17. The method according to claim 16, wherein the voltage requirement threshold is based on a function performed by an apparatus.
 18. The method according to claim 14, wherein the supply voltage is greater than or equal to a threshold voltage of the electronic unit.
 19. The method according to claim 14, wherein the backscatter radiation communicates the supply voltage.
 20. The method according to claim 14, wherein the antenna is disposed on an eye-mountable device. 